Vision [in Opticks]

Vision [in Opticks]

the
physical cause of vision or sight seems to be that the rays of light, striking
on the bottom, of the eye, do there excite certain vibrations in the
Tunica
Retina; which vibrations being propagated, as far as the brain by the
solid
fibres of th Optick Nerves, do there cause the sense of
Seeing.

For
as dense bodies do retain their heat longest, and that in proportion to their
density, they retain it longer as they are more dense; so the vibrations of
their particles are of more durable nature than those of rarer bodies, and can
be propagated to greater distances; wherefore the solid and dense fibres of the
nerves, whose matter is of an homogeneal and uniform nature, are very proper to
transmit to the brain such motions as are impress’d on the external organs of
our senses.

For
that motion, which can preserve itself a good while in one and the same part of
any body, can also be propagated a great way from one part of it to another;
provided the body be of an homogeneal nature, and that the motion be not
reflected, refracted, interrupted, or disturbed by any inequality in that
body.